1. Field of the Invention
The present invention is directed to a method and to a system for regulating the transmission power of a mobile station of a mobile radiotelephone system in which information are transmitted in different carrier frequencies with a frequency hopping method.
2. Description of the Related Art
In order to replace the various analog and digital standards that exist in Europe, the DECT (digital enhanced cordless communication) standard was passed in the early xe2x80x9890xe2x80x99s. It is the first common European standard for cordless telecommunication. A DECT network is a micro-cellular, digital mobile radiotelephone network for high subscriber densities and is mainly designed for use in buildings. Use of the DECT standard, however, is likewise possible outside of buildings. The capacity of the DECT network of about 10,000 subscribers per square kilometer makes the cordless standard into an ideal access technology for network operators. According to the DECT standard, the transmission of data signals is also possible in addition to the transmission of speech. Thus, cordless data networks can also be constructed on a DECT basis.
The DECT standard is explained in greater detail below with reference to FIG. 2. A digital, cordless telecommunication system was standardized for Europe under the name DECT. In combination with the switching function of a telecommunication system, this system is thus suitable for the mobile telephone and data traffic in an office building or on a corporate campus. The DECT functions supplement a telecommunication system and thus turn a switch into the fixed station FS of the cordless telecommunication system. Digital radio connections between the fixed station FS and the maximum of 120 mobile stations MS can thus be set up, monitored and controlled on up to 120 channels.
Transmission on a maximum often different carrier frequencies (carriers) is carried out in the frequency range of 1.88 GHz to 1.9 GHz. This frequency-division multiplex method is referred to as FDMA (frequency division multiple access).
Respectively twelve timeslots are transmitted in chronological succession in the uplink and in the downlink in the time-division multiplex method TDMA (time division multiple access) on each of the ten carrier frequencies. Thus 120 channels derive for the cordless telecommunication according to the DECT standard for ten carrier frequencies, each having twelve timeslots in the uplink and in the downlink. Since, for example, one channel is required for each voice connection, 120 connections to a maximum of 120 mobile stations MS derive. Alternating mode (duplex, TTD) is employed on the carriers. After twelve channels (channels 1-12) have been sent by the fixed station, it switches to reception and receives twelve channels (channels 13-24) from at least one mobile station in the opposite direction.
A time-division multiplex frame is thus composed of 24 channels (see FIG. 2). Channel 1 through channel 12 are transmitted from the fixed station FS to the mobile stations MS, whereas channel 13 through channel 24 are transmitted in the opposite direction from the mobile stations MS to the fixed station FS. The frame duration is 10 ms. 320 bits of information (for example, speech) and 104 bits of control data (e.g., synchronization, signalling and error monitoring data) are transmitted in this time. The payload bit rate for a subscriber (channel) derives from the 320 bits of information within 10 ms, which translate to 32 kilobits per second.
Integrated components that convert the DECT functions have been developed for fixed and mobile stations. The fixed station and the mobile station perform similar functions. One of the integrated modules is the RF module, i.e., the module that implements the actual function of receiving and transmitting in the RF range.
It is known to employ xe2x80x9cfast hoppingxe2x80x9d RF modules, i.e., RF modules that can implement a change of the carrier frequency from one timeslot or, channel to the next. However, these fast hopping RF modules are very complex and expensive, so usually xe2x80x9cslow hopping-RF modules are employed in practice, i.e., modules that require a certain time for changing the carrier frequency. In practice, the time span that the slow hopping RF module requires for the change of the carrier frequency essentially corresponds to the time span of a time slot. This means that an inactive time slot (blind slot) in which no data can be transmitted must follow each active time slot, i.e., each slot in which are transmitted. This means that only six connections can be implemented in practice on a carrier frequency in the DECT standard instead of the twelve connections that are possible.
A DECT channel is defined by its time slot and its carrier frequency. According to the DECT standard, the organization of the reemployment of physical channels ensues with a dynamic channel selection. A complicated frequency planning, as in cellular systems, is thus superfluous. For a connection setup, the signal levels of all channels are continuously measured and the malfunction-free channels are administered in a channel list (channel map). During a connection, the signal levels of all channels as well as the reception quality continue to be measured. When this monitoring shows that the channel employed at the moment was transmitted on a carrier frequency that was disturbed (due, for example, to the influence of a transmission on the same carrier frequency from or to a different fixed station), a different carrier frequency that is entered as disturbance-free in the in the channel list is automatically selected for the next active time slot.
As an alternative, a xe2x80x9cfrequency hoppingxe2x80x9d method in which the carrier frequency is changed after a predetermined time span, for example, one frame of the transmission, can also be employed.
For countries outside of Europe, the DECT standard may have to be modified and adapted to the local conditions. In the USA, for example, the transmission cannot ensue in the normal DECT range between 1.88 and 1.90 GHz; rather, the generally accessible 2.4 GHz ISM (industrial, scientific, medical) band is available. Furthermore, changes would have to be undertaken for adaptation to the national regulations such as the American rule FCC part 15 which describes the transmission methods, transmission powers and the available bandwidth allowed for the air interface.
In the DECT standard, each time slot contains another 104 bits required for the signal transmission in addition to the aforementioned 320 information bits as well as 56 bits of a guard field, so that each time slot contains a total of 480 bits, permitting a data rate of (24xc3x97480 bits)/10 ms=1,152,000 bits/s. This high data rate is not meaningful in the American ISM band since too great a bandwidth would be required per usable channel. Despite these rules, optimally unmodified component parts developed for the DECT standard such as the baseband controller should, for cost reasons, continue to be useable despite these rules.
Since, further, mobile stations are usually battery/storage cell-operated, the energy they consume during operation should be as low as possible in order to enable long operating times.
ETS 300 578: March 1995 (GSM 5.08 version 4.12.0) discloses a system in which a change of the transmission signal power of a mobile part is initiated by exceeding a upward or, downward limit of a signal level threshold by a plurality of values of a signal level measured by the base station as well as exceeding an upward or downward transgression of a quality threshold by a plurality of values of a quality parameter value measured by the base station.
For the mobile radio transmitter/receiver, particularly a mobile part, of a cordless telecommunication system according to German patent document DE 44 26 255 A1, the mobile partxe2x80x94regardless of a reception level evaluation by the base stationxe2x80x94should be independently in the position to regulate the transmission power in order to reduce the power or, energy consumption, so that a maximally possible operating duration derives in the standby or active mode.
The object of the invention is to provide a method and system for regulating the transmission power of a mobile station of a mobile radiotelephone system. This object is achieved by a method for regulating transmission power of a mobile station of a mobile radiotelephone system in which information are transmitted in different carrier frequencies with a frequency hopping method, comprising the steps of: receiving information that are transmitted from a mobile station in a fixed station; detecting a transmission quality of the transmitted information in the fixed station, comprising the following steps in the DECT standard or a similar standard which utilizes a transmission unit having an A-field and an X-field: a) determining whether an error is present in the cyclically redundant bits of the A-field (A-CRC error); b) determining whether an error is present in the cyclically redundant bits of the X-field (X-CRC error); c) determining whether a data packet has been lost; and d) determining whether a value of a radio signal strength indicator (RSSI value) lies below a specific threshold; the method for regulating transmission power further comprising the steps of: transmitting a first message to the mobile station for lowering the transmission power when the determinations under steps (a)-(d) are all negative and the transmitted information were transmitted with a high transmission power; and transmitting a second message to the mobile station for raising the transmission power when one or more of the determinations under steps (a)-(d) are positive and the transmitted information were transmitted with a low power. The inventive method may also further comprise the steps of lowering, by the mobile station, its transmission power when it receives the first message; and raising, by the mobile station, its transmission power when it receives the second message.
This object is also achieved by a system for regulating transmission power of a mobile station of a mobile radiotelephone system in which information are transmitted in different carrier frequencies with a frequency hopping method, comprising: a mobile station; a fixed station, the fixed station comprising: a receiver fashioned such that information that are transmitted from the mobile station are received; a detector in the DECT standard or a similar standard which utilizes a transmission unit having an A-field and an X-field, the detector comprising: a) an A_CRC error determination mechanism fashioned such that an error in the cyclically redundant bits of the A-field is detected; b) an X-CRC error detection mechanism fashioned such that an error in the cyclically redundant bits of the X-field is detected; c) a packet loss determination mechanism fashioned such that a data packet that has been lost is detected; and d) a threshold determination mechanism fashioned such that exceeding a downward threshold of a value of a radio signal strength indicator is detected the fixed station further comprising: a transmitter fashioned such that a first message is transmitted to the mobile station for lowering the transmission power when all mechanisms (a)-(d) make a negative finding and the information were transmitted with a high transmission power, and a second message is transmitted to the mobile station for raising the transmission power when at least one of the mechanisms (a)-(d) makes a positive finding and the information were transmitted with a low transmission power. The mobile station may also comprise a mechanism for lowering its transmission power when it receives the first message and for raising its transmission power when it receives the second message.
The inventive method as well as the inventive system for the regulation of the transmission power of a mobile station are employed in a mobile radiotelephone system in which information are transmitted in different carrier frequencies with a frequency hopping method. The inventive system comprises a mechanism for receiving information transmitted from a mobile station in a fixed station. Additionally, a mechanism is provided for detecting the transmission quality of the transmitted information in the fixed station. When he transmission quality is good and the information were transmitted with a high transmission power, a first message for lowering the transmission power is transmitted to the mobile station. When the transmission quality is poor and the information were transmitted with a low transmission power, a second message for increasing the transmission power is transmitted to the mobile station. According to the present invention, the transmission power employed in the mobile station for the transmission of information to a fixed station is adapted dependent on the quality of the transmitted information. When the transmission quality is adequate, then a low transmission power can be employed in the mobile station, as a result of which the energy used in the mobile station can be considerably lowered.
The mobile station comprises mechanism for lowering the transmission power when it receives the first message and for increasing the transmission power when it receives the second message.
Advantageously, the mechanism for detecting the transmission quality of the transmitted information in the fixed stationxe2x80x94when the mobile radiotelephone system is operated on the DECT standard or a similar standardxe2x80x94comprises mechanism for identifying whether an error is present in the cyclically redundant bits of the A-field (A-CRC error), mechanism for determining whether an error is present in the cyclically redundant bits of the X-field,(X-CRC error), mechanism for determining whether a data packet has been lost, and mechanism for determining whether the radio signal strength indicator (RSSI value) lies below a specific threshold.
When at least one of the mechanism makes a positive finding, the detection mechanism decides that the transmission quality is poor. When all of the mechanism make a negative finding, the detection mechanism determines that the transmission quality is good.
The high transmission power employed by the mobile station can, for example, be a maximum transmission power of a few hundred mW, whereas the low transmission power can, for example, be a few tens of mW.